Aircraft surface operations involve taxiing of an aircraft from a terminal gate (or generally from the ramp or apron area) to an assigned runway in preparation for takeoff, or movement of an aircraft from a runway to a terminal gate after landing. Taxi instructions, at towered, control airports, are verbally issued by ground control using radio-telephony to the aircraft. When an aircraft taxies across the airport, it travels on a series of assigned taxiways based on directions received from a ground controller. Ground controllers at busy airports may be directing the movement of several dozen aircraft at any particular time. A taxiing aircraft will often have to travel across active runways to reach its destination; therefore, it is critical to coordinate surface operations with takeoff/landing instructions to prevent runway incursions. A runway incursion is “any occurrence in the airport runway environment involving an aircraft, vehicle, person, or object on the ground that creates a collision hazard or results in a loss of required separation with an aircraft taking off, intending to take off, landing, or intending to land” (Runway Safety, Federal Aviation Administration, available at http://www.faa.gov/runwaysafety/). Even when there is no risk of collision, an aircraft taking off or landing on the wrong runway can result in a crash if the actual runway used is too short to accommodate the aircraft.
Ensuring that an aircraft uses the correct, safe route from the gate to the runway (and vice versa) requires both that the ground controller provide correct instructions to the aircraft and that the aircraft precisely follow those instructions. Signs and other markings help a pilot identify the taxiways and runways. These signs and markings may be confusing, especially to a relatively inexperienced pilot or to a pilot at an unfamiliar or confusing airport. Further, reduced visibility at night or during inclement weather can cause a pilot to misread or fail to see these signs and markings.
To assist in surface operations, pilots utilize airport maps. These maps were traditionally paper charts. However, pilots can now utilize an electronic moving map or “electronic flight bag” (EFB), which displays a digitized map of the airport. The EFB may be coupled with the aircraft's navigation system such that the aircraft's current position is displayed on the map, thereby enabling the pilot to readily see if the aircraft is on the assigned taxiway/runway, and to anticipate turns.
During surface operations, it is also critical that the pilot watch for other aircraft and service vehicles (such as catering trucks) which are nearby and may constitute a collision hazard. This is particularly important when visibility is reduced. As such, it is desirable that a pilot minimize the percentage of taxiing time spent looking down at charts, instruments, or the like, and maximize the percentage of time spent looking out the windshield (also termed windscreen). While a pilot is looking down at charts, etc., the pilot is said to be “heads-down.” While a pilot is looking out the windshield, the pilot is said to be “heads-up.”
During surface operations, it is also critical that the pilot(s) listen for their aircraft call sign for updates, modifications, revisions, or other changes to taxi clearance. The potential for a collision hazard exists if the pilot(s) do not receive the new clearance instructions or misunderstand the taxi clearance due to errors of omission or commission. Due to the quality of Very High Frequency (VHF) radio telephony currently used for airport surface operations, a significant hazard exists for mistakes made during read-back, callback, and hear-back of taxi instructions. During restricted visibility or other conditions that significantly increase workload for the pilot(s), the incidence of these types of occurrences and potential consequences increase, particularly for long or complex taxi clearance. Pilots may be “heads-down” during receiving and copying of taxi clearances.
One known technology for displaying navigational and safety information within an aircraft is a heads-up display (HUD). The HUD projects information onto a transparent display screen, such that the pilot can see the projected information while also having an unobstructed view outside the aircraft. This information can be of great value to a pilot, particularly in low visibility situations. However, there are several drawbacks of the HUD. The HUD has a limited field of view (typically 30 degrees horizontal by 24 degrees vertical), so that objects outside of this field of view cannot be represented. Additionally, HUDs only project a monochromatic (typically green) display, thereby preventing the use of multiple colors to help make a crowded display more readable. HUDs are also typically quite expensive, and must be integrated into the airframe of an aircraft.